A. Technical Field
The present invention relates to systems for ranging and determining locations of objects, and more particularly, to systems for determining distances based on measured time of flights.
B. Background of the Invention
A simple ranging system, such as radar, is composed of an interrogator and a reflector. The distance to the reflector is determined by measuring the time of flight of a signal transmitted from the interrogator to the reflector and back to the interrogator. The time of flight will then represent twice the distance between the interrogator and the reflector. An advanced ranging system, however, requires authentication and data communication between the interrogator and the reflector that cannot per definition, remain a simple reflector, but a transponder capable of authentication, receiving, processing and retransmission of data.
Since, in ranging and location determination, the propagation times of the signals are among the essential data that determine range and location, in such applications, there is a fundamental need to maintain a tight control over actual propagation times. To do so, all other delays, e.g. processing times, in the forward and backward links as well as inside the transponders, need to be accounted for. The conventional ranging systems have difficulty in measuring these delays due to unpredictability and unreliability. Thus, there is a need for a system that has a mechanism for eliminating these delays, to thereby enhance the accuracy in determining the propagation times of the signals.